HOW TO KNOW THE FRESH-WATER ALGAE 



28b Envelope with 2 overlapping sections which do not show except 

 when the cell is in the process of dividing; envelope 4-angled when 

 seen from the 'front.' Fig 24 PTEROMONAS 



Fig. 24. Pteromonas aculeata Lemm. 



This genus takes its name from the winged 

 appearance of the envelope. Although there 

 are about 7 species known, the most common 

 perhaps is Pteromonas aculeata Lemm. recog- 

 nizable by the rectangular appearance as seen 

 in 'front' view. Like Phacotus (Fig. 23) this spe- 

 cies sometimes occurs in the plankton of rivers. 

 See Scotiella (Fig. 127), a genus which has been 

 regarded by Pascher as belonging to Pteromo- 

 nas. 



Figure 24 



29a (26) Cells elongate or fusiform. Fig. 25 CHLOROGON1UM 



Fig. 25. Chiorogonium sp. 



Of the 8 species known for this genus only 2 are 

 reported from the United States. They are all more 

 elongate than any other members of the order Volvo- 

 cales. Usually found in swamps and shallow ponds, 

 they sometimes appear abundantly in laboratory 

 aguaria. 



Figure 25 

 29b Cells round, oval or angular 



30 



30a Cell wall with lump-like protuberances or short lobes. Fig. 26 



LOBOMONAS 



Fig. 26. Lobomonas rostrata Hazen. 



The irregular lumpy appearance of this genus is 

 its chief characteristic. The organisms appear in the 

 same habitat with Haemafococcus (Fig. 19), i.e., tem- 

 porary rain water pools and cement basins. 



Figure 26 



33 



